1985
? Last satellite decommissioned in 1995
– Block II/IIA launched 1989-1997
? 4 atomic clocks
? Increased satellite lifetime ? More data storage capabilities ? Nuclear detonation detector
– Block IIR
? Ability to operate autonomously for long
periods
? Up to 5 carrier signals
Current GPS Capabilities
? The current system employs 24 active satellites, at least 6
backups ? Cost to maintain system: $750 million per year
– Combination of Block II, IIA and IIR
– 1995 use of GPS became available to the public, free
of charge
– Levels of service:
? SPS channel L1
– Predicted accuracy: 13 m horizontal,
22 m vertical, 200 ns
? PPS channel L2
– Predicted accuracy: 8 m horizontal
and vertical, 40 ns
3.1.4 Other Systems GLONASS
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? Global Navigation System developed by Russia ? Nominally consists of 21 satellites plus 3 spares
? 8 satellites arranged in 3 orbital planes with an inclination
of 64.8o ? Orbits are approximately circular with a period of 11h 15m ? ? ? ? ? ? ? ? ?
Also transmits L1&L2 carriers, C/A & P codes L1 is in 1602-1615.5 MHz band
To be shifted to (1598.0625-1604.25 MHz) L2 is in 1246-1256.5 MHz band
To be shifted to (1242.9365-1247.75 MHz) C/A code is 0.5Mps P Code is 5.11 Mbps Carrier frequency depends on the satellite Each one is currently unique
After shift, each pair of satellites will be assigned the same frequency
? Pairs on opposite sides of the Earth (antipodal)
? Uses frequency channel rather than code to identify
satellite ? ? ? ?
The system is not as robust as predicted Fewer satellites in orbit than expected As little as 7 in May 2001
New class of satellites (GLONASS-M) should be launched soon
? Can be used in conjunction with GPS to improve
navigation/positioning ? Need to account for 2 differences in reference
? Need to transform Earth Parameter System 1990 (PZ-90)
to WGS 84
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? Can differ by up to 20 m
? Need to relate Russian time scale to GPS time ? Can differ by 10s of μs Beidou北斗系统
S1 S2 DS1 DS2 D1 D2 地面中心站 用户 ? Chinese regional satellite navigation system ? Consists of 2 satellites in geostationary orbits
– Altitude of 36000 km
? Used in land and marine transportation ? Plans for next generation system Galileo System伽利略系统
? Positioning Accuracy: 10m (95%); ? Timing Accuracy: < 33ns; ? TTFF : < 15s;
? Global Availability: >99.7%; ? 30 satellites; Galileo
? Proposed and being planned by Europe
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? It will be controlled by civilians
? Plans call for 30 medium Earth orbit satellites ? Distributed in 3 orbital planes
– Altitude of 23000 km
? Will provide 2 levels of service
– Basic (free-of-charge) – Chargeable service
? 3 phases of development
– Definition phase (already completed) – Development and validation phase – Deployment phase
? Scheduled to begin in 2006/7 timeframe ? Service by 2008 (?)
? Because it is civilian operated, it will have advantages in
the marketplace ? Already promising to provide a service that will meet
legal standards
– GPS can’t do this
? If the lawyers are happy, the business money is more
likely into Galileo products
WAAS
? Wide Area Augmentation System (WAAS)
– Covers North America
– South America could be covered later
? Utilizes GPS but augments it with additional satellite
information
– Use geostationary satellites
? International Maritime Satellite
– Provides additional reliability and accuracy
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? Used for aircraft navigation
– Not necessarily for takeoff and landing
LAAS
? Local Area Augmentation System (LAAS)
? Utilizes GPS but augments it with pseudolite information
at critical locations
– Typically around airports but could be used in
other locations theoretically
? Used for aircraft takeoff and landing
– Including category II/III
EGNOS
? European Geostationary Navigation Overlay System
(EGNOS) ? European version of WAAS
– Covers all of Europe and North Africa
– Could be extended to cover all of Africa and
Middle East ? Will eventually be superseded by Galileo MSAS
? MTSAT Satellite-Based Augmentation System (MSAS)
– Multi-functional Transport Satellite (MTSAT)
? Japanese version of WAAS
– Covers parts of Asia and the Pacific 3.2 GPS System Composition
The Global Positioning System
? Constellation of 24 satellites operated by the U.S.
Department of Defense
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